1. Field of Invention
The present invention relates generally to apparatus embedded in and or applied to gasket structures, and particularly to sensing apparatus applied to combustion gaskets of internal combustion engines. More specifically, the invention relates to pressure sensing apparatus for measuring pressure levels of combustion gases that are provided within structures of cylinder head combustion gaskets.
2. Description of the Prior Art
It is known to employ electronic sensors in gaskets for sealing between engine components including, for example, the block and cylinder head of a multi-cylinder internal combustion engine. In one such case, the gasket comprises a sealing plate having several combustion chamber orifices, with combustion chamber sealing elements situated on the edges of the sealing plate surrounding the combustion chamber orifices. The gasket includes sensor elements for cylinder-specific detection of sealing movements perpendicular to the plane of the sealing plate, caused by pressure changes in respective combustion chambers being measured. All of the sensor elements are arranged outside of the combustion chamber sealing elements, and can be piezoelectric and piezoresistive, as well as glass fiber light guide-style sensors.
In another example, a gasket enclosed sensor system is employed for measurement of combustion chamber parameters and delivery of signals to points external of the engine. The gasket includes a combustion opening substantially surrounding a combustion chamber, and includes an access opening extending from the combustion chamber to a point external of the engine. A metallic sensor terminal is positioned within the access opening, and insulating material substantially surrounds the metallic sensor terminal.
In yet another example, a fluid sensor and associated circuitry are used to indicate presence of oil flow in a multi-cylinder internal combustion engine. The oil sensor includes a heating element positioned within the oil line, directly in the oil flow path. A comparator measures the value of signals from upstream and downstream heat sensors, and triggers a switching circuit when the temperature at the sensors approach one another to indicate an adequate oil flow to the engine.
In still another example, a gasket formed in the shape of an exhaust flange includes a load sensor comprising a pressure sensitive electrically resistive material positioned between electrodes and conductors extending outwardly of the perimeter of the gasket. A seal provided between first and second layers of the gasket, and about the load sensor, provides a seal for the electrodes, which are positioned in a cavity to protect the sensor from fluids.
The present invention is a multi-layer steel (MLS) cylinder head gasket containing at least one fully integrated pressure sensor. The gasket comprises first and second steel metal layers having inner and outer surfaces, with their inner surfaces substantially facing one another. A third metal layer acts as a spacer layer; the spacer layer is interposed between and contacts the inner surfaces of the first and second layers. In the described embodiment, the outer surfaces of the first and second layers include an elastomeric seal coating, while the inner surfaces of the first and second layers include a friction reducing coating.
The cylinder head gasket further includes combustion apertures that extend through each of the three described layers, thus contiguously between the outer surfaces of the first and second metal layers. The combustion apertures circumscribe the cylinder bores. The gasket also includes pressure sensors, for example strain gauges that are provided with protective slots formed in the spacer layer adjacent to but spaced from each of the combustion apertures. Once the gasket has been installed between a cylinder head and engine block, the strain gauges are adapted to measure deflection of a wall of each of the slots resulting from pressure changes occurring within the combustion chambers. For this purpose, the measured strains are correlated to pressure changes within the combustion chambers to generate an appropriate electric signal.
One particular advantage of the disclosed MLS gasket is that the strain gauges are not directly exposed to combustion gases that might otherwise foul the sensor. As disclosed, the sensor is adhesively contained on an arcuate wall of the described protective slot. Sensor wires are attached to the strain gauges; the wires are carried in grooves formed into the spacer layer. For accommodating a plurality of cylinders, wires from each cylinder bore are bundled into a common groove of the spacer layer. In an alternately described embodiment, the spacer layer can extend beyond the normal boundary of the gasket. Thus, the spacer layer may be extended radially outwardly of a conventional gasket component perimeter in environments where such extension may be useful or desirable. Finally, a converter may be employed to change optical signals into electrical signals for appropriate transmittal to a microprocessor of an engine control module, if for example an optical strain gauge is employed.